Piping systems designed for high temperature fluids usually require specialized seals at various points in the system. Such points may be found where a connection is made between two or more adjacent piping sections and/or where a component is connected to a section of pipe. A specialized type of flexible connection is present in many systems to enable the system to compensate for movement or misalignment between the system's pipes and/or connected components. An example of a system that typically employs a flexible connection in the form of a flexible coupling (also known as a flexible joint) is the bleed air system used in jet aircraft. The system distributes bleed air from a jet engine through a duct system to accomplish various functions, such as engine cooling and bleeding, cabin temperature control or de-icing of portions of the plane's exterior surface. It should be noted that the words pipe, duct, conduit, tube and tubular structure are all herein broadly defined as any tubular structure, or even cylindrical opening, through which a fluid can travel, and are considered equivalent and may be used interchangeably.
Typically, a bleed air system will employ at least one flexible joint to connect adjacent duct sections, or to connect a section of duct to a component. The joint includes structure that enables it to compensate for misalignments of the ductwork, elongation or contraction of the ductwork brought about by temperature changes, and/or movements of the engine or aircraft structure due to various factors including vibration, changes in engine speed and/or loading, and air turbulence.
In the prior art, a number of different seals have been employed in flexible couplings used in aircraft bleed air systems. Since the air flowing through the system can have a temperature of almost 600 degrees Fahrenheit, most prior art seals deployed in such a system are made of a heat-resistant material such as a specialized silicone or PTFE (also known as, and used herein interchangeably with, Polytetrafluoroethylene and TEFLON). These prior art seals typically feature a generally rectangular cross-section, with perhaps a crowned outermost surface to maximize their sealing effectiveness. An example of a flexible joint used in a bleed air system is taught by Camacho et al in U.S. Pat. No. 5,106,129 entitled Flexible Coupling for Transferring a Fluid Between Two Fluid Conduits. In the Camacho et al patent, it is noted that the crowned surface of prior art seal rings can wear down due to vibration and rubbing. Once worn, the seal can lose its effectiveness and allow fluid leakage. It is also well known in the art that prolonged exposure to high-temperature air can cause a seal made of a silicone material to become brittle and burnt, with a resultant loss of integrity that leads to fluid leaking past the seal. Once the fluid, high temperature air in a bleed air system, gets past the seal, the fluid will cause increased noise and reduced efficiency. A leaking seal must eventually be replaced, a process that can be both costly and time consuming.
To overcome the above-described problems, it is known to fashion seals from PTFE with various modifications to improve the seal's flexibility, durability and life expectancy. An example of such a seal is taught in my prior, U.S. Pat. No. 6,179,339, entitled Seal Rings for Low Loss Flexible Coupling of Gas Conduits. In the patent, I discuss the noted problems with prior art seals and teach the use of a pair of grooves in a PTFE seal ring to enhance the seal's flexibility. The seal ring is used in combination with a garter spring whereby the spring continuously applies pressure on the seal ring to maintain and maximize the seal's contact with adjacent structure. When the seal ring is to be used in an expansion mode, where the spring applies an outward force on the seal ring, I teach the use of a Marcel spring with the seal ring. However, a typical installation of the seal ring requires that the seal ring be cut, thereby affecting the seal's integrity and creating a potential leak path.
It is also known in the seal art to employ seal rings that have an ‘L’-shaped cross-section. Installation of this type of seal, if the seal is made of a substantially rigid material such as PTFE, can be difficult and normally requires that the seal be cut, with a consequent adverse affect on the seal's integrity and the creation of a potential leak path.